openSDA with Segger FRDM K64

Until now I've been using the segger Jlink flasher cable. I've now working with a new board and went back using the original usb cable with the OpenSDA interface (in the device manager: JLink CDC UART Port). For some reason I cannot connect to the board and flash it.

I've used all the available options (Segger, obviously, PEMicro and OpenOCD), I've tried with the MBED bootloader and the Segger bootloader (also with my old FRDM K64 board and a new FRDM K64 board). I've tried the SWD button as well as the JTAG button (in the SEGGER config window).

Surely I'm doing something wrong..

What have I forgotten?

Using the SEGGER:

Connecting to target...ERROR: Could not connect to target.Target connection failed. GDBServer will be closed...Restoring target state and closing J-Link connection...